Where the telescope ends, the microscope begins. Which of the two has a grander view?
— Victor Hugo, Les Misérables, “Saint-Denis”, bk. III, ch. 3
The average adult human body has been estimated to contain upwards of 37 trillion cells. That is represented by the number 37 followed by 12 zeros. For comparison, the Milky Way galaxy has anywhere between 100 billion and 400 billion stars (I suppose astronomers may be forgiven the lesser precision). At the upper end of that estimate, the number is 4 followed by 12 zeros. A rough ‘guestimation’, therefore, is that there are approximately nine times as many cells in a human body as stars in our galaxy. Consider also that these myriad cells constitute a living, breathing, organized ‘ecosystem’, which, if it is to collectively survive, must both maintain order and adapt to changes in the external environment, a task requiring a phenomenal degree of communication and coordination. At the intersection of these physical and chemical processes is the discipline of physiology.
For various reasons, this human ecosystem does not always remain in balance; the result is disordered physiology, or pathophysiology. The potential causes of such disordered physiology or disease are many. However, it is possible to make some broad and not inaccurate generalizations. One of my favourite professors and mentors, a physician/scientist/musician/social activist by the name of Dr. David Bruce Stewart, made this insightful observation: most disease processes can be categorized as being the result of one or more of infection, inflammation, neoplasia, or trauma. One can argue with the completeness of this list, or whether it truly encompasses the myriad different disorders; however, in looking at almost any specific disease, you will find elements of at least one of the above-listed processes.
My intent in writing this short book is to share with you, the reader, my fascination with both ordered and disordered physiology, as well to provide an approach to this broad topic that I have found useful during my 30 years as an educator and a life scientist. Given that the topic of pathophysiology is so broad, and the scope of this brief book is narrow, I was forced to make some hard choices about what to include. One assumption I’ve made is that most readers would appreciate a ‘ground-up’ approach. This means that an understanding of the content does not require more than a basic high school education (which may or may not have been completed some time ago!). Therefore, this book begins with Chapter 1, “Homeostasis, Control Systems, and Cellular Communication“. In this chapter, we explore the notion that cells are the basic units of life, and that homeostasis depends on cellular communication and control systems. Chapter 2, “Cell and Tissue Adaptation, Injury, and Death“, tackles how cells and tissues adapt to changes in the environment, either successfully or unsuccessfully. The focus and title of Chapter 3 is “Inflammation and Immunity“. In this section, I discuss how the body has multiple protective mechanisms against ‘non-self’, which can be either non-specific and rapid, or very specific and slower. Finally, in Chapter 4, “Cancer“, I endeavor to describe some of the main characteristics of benign and malignant tumours, as well as some of the presumed mechanisms.
Throughout this book, I have included numerous graphics, self-study questions, and links to videos I have created. This is based on the premise that each of us has unique ways of learning, and that a choice of media and learning strategies would best serve to convey this material. By the end of this book, my hope is that you will find yourself with a background and an approach to pathophysiology that is sufficient for the task of understanding specific disease processes.
